1. Field of the Invention
The present invention relates generally to imaging systems, and more particularly, but not exclusively, to imaging systems using micro electromechanical system (MEMS) devices.
2. Description of the Background Art
Arrays of light-modulating elements have been applied to imaging systems, such as display and printing systems. The light-modulating elements may comprise, for example, Grating Light Valve™ (GLV™) light-modulating elements available from Silicon Light Machines of Sunnyvale, Calif. For example, a two-dimensional image may be projected onto a screen using one or more linear arrays of light-modulating elements. In such display systems, a linear modulator array modulates an incident light beam to display pixels along a column (or, alternatively, a row) of a two-dimensional (2-D) image. A scanning system is used to move the column across a projection screen such that each light-modulating element is able to generate a row of the 2-D image. In this way, the entire 2-D image is displayed.
Publications describing light modulator devices and their applications include, among others: “The Grating Light Valve: Revolutionizing Display Technology,” by D. M. Bloom, Projection Displays III Symposium, SPIE Proceedings, Volume 3013, San Jose, Calif., February 1997; “Grating Light Valve Technology: Update and Novel Applications,” by D. T. Amm and R. W. Corrigan of Silicon Light Machines in Sunnyvale, Calif., a paper presented at the Society for Information Display Symposium, May 19, 1998, Anaheim, Calif.; “Optical Performance of the Grating Light Valve Technology,” David T. Amm and Robert W. Corrigan of Silicon Light Machines, a paper presented at Photonics West-Electronics Imaging, 1999; “Calibration of a Scanned Linear Grating Light Valve Projection System,” R. W. Corrigan, D. T. Amm, P. A. Alioshin, B. Staker, D. A. LeHoty, K. P. Gross, and B. R. Lang, a paper presented at the Society for Information Display Symposium, May 18, 1999, San Jose, Calif.; “An Alternative Architecture for High Performance Display,” R. W. Corrigan, B. R. Lang, D. A. LeHoty, and P. A. Alioshin of Silicon Light Machines, a paper presented at the 141st SMPTE Technical Conference and Exhibition, Nov. 20, 1999, New York, N.Y.; “Breakthrough MEMS Component Technology for Optical Networks,” Robert Corrigan, Randy Cook, and Olivier Favotte, Silicon Light Machines—Grating Light Valve Technology Brief, 2001; and U.S. Pat. No. 6,215,579, entitled “Method and Apparatus for Modulating an Incident Light Beam for Forming a Two-Dimensional Image,” and assigned at issuance to Silicon Light Machines. Each of the above-mentioned publications is hereby incorporated by reference in its entirety.
In printing applications, image data can be scanned across print media to create exposure and 2-D images, or the print media can be moved across a fixed, modulating one-dimensional (1-D) line of light. For example, a laser beam may be bounced off a reflective surface of a light modulating element and onto a plate, which may be on a rotating drum. The laser beam has a power density sufficient to expose the plate. The light modulating elements are actuated to modulate the laser beam and form a pattern on the plate. The plate is inked and rolled onto paper to transfer the pattern thereon. Examples of other printing applications involving light modulators include integrated circuit (e.g., lithography), liquid crystal display (LCD), and printed circuit board (PCB) fabrication.
One problem with using a scanned-linear array in display systems, such as those using a 1-D light modulator array, is that it is difficult to achieve perfect alignment of all three primary colors namely, red, green, and blue (RGB). Each color is modulated from a separate light modulator array and is optically combined to overlap in exactly the same location on a screen. In the vertical (array) direction, the pixel locations are defined by the location of the arrays themselves. The alignment in this direction needs to be precise and is controlled almost entirely by the mechanical alignment of the arrays. In the horizontal (scanning) direction, the pixel location may be determined by several factors, including mechanical alignment of the arrays, the location of the optical illumination, and the timing of the supporting electronics. Pixel alignment is also an issue in printing applications because some printing applications involve multiple colors and/or arrays, or may require multiple passes for exposure averaging, bit depth, or improved resolution. Some printing applications may also involve “stitching” the outputs of multiple arrays end-to-end to form a longer 1-D swath, for example.
FIG. 1 shows a “bow” or convergence problem resulting from misalignment of red, green, and blue colors in display applications. In the example of FIG. 1, three linear 1-D light modulator arrays (one array per color) are oriented vertically, and the horizontal axis represents the scanning direction. In most cases, the convergence problem shown in FIG. 1 cannot be fully corrected by purely mechanical alignment. Because some imaging system color convergence specifications are in the range of ±0.1 pixel to ±0.5 pixel, a more robust solution to this misalignment problem is needed.